Electropolymerization of Pyrrole and Electrochemical Study of Polypyrrole. 2. Influence of Acidity on the Formation of Polypyrrole and the Multipathway Mechanism

Abstract

Potentiodynamic generation of polypyrrole films at an extremely low reaction rate causes the resulting material to show an additional oxidation wave that is more negative and sharper than the one normally observed. The additional peaklike oxidation wave belongs to an unknown structural entity PPy(II). The treatment of acetonitrile with basic alumina prevents its formation, whereas the addition of a low concentration of hydrochloric acid (10 -5 to 5 × 10 -5 M) to the acetonitrile electrolytic solution promotes its formation. However, higher concentrations of HCl (>10 -4 M) results in the disappearance of the characteristic peaks of both PPy(II) and the conventional PPy(I). Instead, following the acid-catalyzed trimerization of pyrrole, an ill-defined, structurally changeable, and partially conjugated PPy(III) from electrochemical side reactions may be deposited on the electrode. In a solution of high acidity, the application of a low potential to the electrolysis passivates the electrode, owing to the formation of nonconductive PPy(III) with a low degree of conjugation. A schematic mechanism for several possible pathways of pyrrole polymerization is proposed.

Electrochemical Deposition of Hollow N-Substituted Polypyrrole Microtubes from an Acoustically Formed Emulsion

“…Studies have shown that the rate of polymerization of pyrrole increases under acidic conditions. 43 TEM micrographs recorded of individual tubes show that the hollow cavity extends the entire length of the structure ( Figure 6a). It also confirmed that the tube morphology remained intact despite being removed from the surface and sonicated, indicating high structural stability.…”

Characterization and corrosion performance of poly(pyrrole-siloxane) films on commercial Al alloys

“…H 2 deformation [35] (pointed by arrows in Fig. 6b, c), which would explain the low doping level as a consequence of partial chain saturation [29]. However, it is clear that under similar synthesis conditions degradation reactions are suppressed compared with Ppy/AA6082.…”

“…490 cm -1 , indicate that the polymer chains consist principally of hydroxipyrrolidines and partially saturated pyrrolidines [27,28]. These functionalities, probably resulting from acid-catalyzed degradation reactions during Py electropolymerization in the aqueous synthesis medium [29][30][31], disrupt Ppy conjugation resulting in a less doped polymer. Similar reasoning cannot be applied to Ppy/AA5083 and Ppy/AA2024 that exhibit higher quality film structure (Fig.…”

The Incorporation of Bovine Serum Albumin into a Polypyrrole Film in One Simple Step

“…Nevertheless, at a pH of 12.0, the currents obtained from the voltammograms were considerably lower and after cycle 5 there is evidence of a further drop in the current, Figure 8b, indicating poor stability in this highly alkaline solution. This is due to a loss in conductivity (29,30), to give more insulating polymer films and the decrease in current could arise from both the nature of the polymer film and the BSA (31,32). …”